Improve names and types in Rust stdlib scraper

[cpmsmith]

This is a follow-up to #2569, addressing issues with the standard library scraper I mentioned here.

There are two main fixes:

1. Names: all pages except for modules' index pages ignored what module they were from, and were just prepended with std::. This meant there were 13 pages named std::Iter, about structs named Iter from different modules. It also meant that things outside modules, e.g. primitive types, were prefixed with std::, naming the page on bool as std::bool, although it can't be referenced that way in code. This also means that there are two pages named std::char - one for the module, and one for the primitive type char.

   This prefixes everything in a module with that module's path, and does not prefix primitives. It also includes submodules in the path.

   For example:

   Before	After
   std::fn	fn
   std::Iter	std::option::Iter
   std::MetadataExt	std::os::linux::fs::MetadataExt

2. Types: almost everything was filed in std, with the exception of modules' index pages and primitive types. This meant there were over 30,000 pages in the std type, and many types for modules with only one page in them.

   This creates types for each module which include all submodules, and files anything not in a module, e.g. primitive types, in std.

   For example:

   Before	After
   std::bool / std::bool	std / bool
   std / std::Iter	std::option / std::option::Iter
   std / std::MetadataExt	std::os / std::os::linux::fs::MetadataExt

Or, in screenshots – before:

and after: